Issues/200: add ability to use different codecs for different messages but for the same client

[komuw]

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Answer the following questions,

What(What have you changed?)

• Add ability to use different codecs for different messages while using the same naz client.
  With this change, message encoding is now a property of the message and not the client.

Why(Why did you change it?)

• Fixes: ability to use different codecs for different messages but same client #200

References:

[komuw]

type checking maybe held back by:

• codecs.CodecInfo not type checked correctly due to a Callable not matching a callback protocol google/pytype#574
• codecs.CodecInfo not type checked correctly python/mypy#8732